Facultad de Medicina Veterinaria y Zootecnia, Universidad Autónoma de Sinaloa, Culiacán, Sinaloa, 80260, México.
Instituto de Ciencias Agrícolas, Universidad Autónoma de Baja California, Ejido Nuevo León, Baja California, 21705, México.
Trop Anim Health Prod. 2022 Mar 30;54(2):152. doi: 10.1007/s11250-022-03152-4.
Heat stress is a great challenge for feedlot operations established in arid zones. The aim of this study was to evaluate if increasing shade area in the pen improved physiological and productive variables in feedlot heifers under hot climate. A total of 510 European and Zebu heifers were randomly assigned to six pens which were divided in two treatments: (1) three pens with 100 heifers each with a shade area of 2.7 m/head (control group [C]); and (2) three pens with 70 heifers each with a shade area of 3.7 m/head (treated group [T]). Physiological variables respiratory frequency (RF) and body surface temperature (BST) of several anatomic regions were taken from 30 heifers per treatment (i.e., 10 heifers/pen). Feed intake on pen basis was recorded weekly and heifers were individually weighted on days 1, 26, and 66 of the study to calculate performance variables. Relative humidity (RH) and ambient temperature (AT) were recorded and used to estimate the temperature-humidity index (THI). Data was analyzed with analysis of variance. The average THI during the study was 81.7 units, which was categorized as dangerous heat stress. In both shaded areas, European heifers showed higher (P < 0.05) RF than Zebu heifers. In the afternoon, the temperature of head, neck, loin, paddle, and belly was higher (P < 0.05) in C compared with T. Heifers under T showed better (P < 0.05) daily weight gain (DWG), total weight gain (TWG), feed conversion (FC), and feed efficiency (FE) than heifers in C, with no effect on dry matter intake (DMI). Results indicate that during hot summer months, Zebu showed more tolerance to heat stress than European heifers; however, heifers under a shade area of 3.7 m/head had better productive performance than those under a shade area of 2.7 m/head during the finishing phase of the feedlot. Increasing the shade area in the finishing phase of beef cattle on feedlot improved some physiological and productive responses during heat stress.
热应激是干旱地区牛场面临的巨大挑战。本研究旨在评估在炎热气候下，增加牛舍内的遮荫面积是否能改善育肥牛的生理和生产性能。共有 510 头欧洲和瘤牛小公牛被随机分配到 6 个牛舍中，每个牛舍分为两个处理组：（1）3 个牛舍，每个牛舍有 100 头小公牛，遮荫面积为 2.7 m/头（对照组 [C]）；（2）3 个牛舍，每个牛舍有 70 头小公牛，遮荫面积为 3.7 m/头（处理组 [T]）。对每个处理组的 30 头小公牛进行了呼吸频率（RF）和几个解剖区域的体表温度（BST）的生理变量测量（即，每个牛舍 10 头小公牛）。每周记录牛舍的采食量，在研究的第 1、26 和 66 天对小公牛进行个体称重，以计算生产性能变量。记录相对湿度（RH）和环境温度（AT），并用于估计温度-湿度指数（THI）。数据采用方差分析进行分析。研究期间的平均 THI 为 81.7 个单位，属于危险的热应激水平。在两个遮荫区域，欧洲小公牛的 RF 均高于瘤牛小公牛（P<0.05）。在下午，头部、颈部、腰部、肩部和腹部的温度在 C 组中高于 T 组（P<0.05）。T 组的小公牛的日增重（DWG）、总增重（TWG）、饲料转化率（FC）和饲料效率（FE）均优于 C 组的小公牛（P<0.05），而干物质采食量（DMI）没有差异。结果表明，在炎热的夏季，瘤牛对热应激的耐受性强于欧洲小公牛；然而，在育肥后期，当遮荫面积为 3.7 m/头时，小公牛的生产性能优于遮荫面积为 2.7 m/头时的小公牛。在育肥后期增加牛舍的遮荫面积，改善了热应激期间一些生理和生产性能的反应。
